[plt-dev] Release Announcement for v4.2.3

Candidate release announcement items below.
----------------------------------------------------------------------
* added support for changing toolbar buttons based on the #lang line,
  use that for #lang scribble/base

* 2htdp/universe stuff

* Several new kinds of promises

* added `path-up' to scheme/require

* syntax/parse extensions (~var, ~literal, ~and, ~not, etc)

* Adding check-member-of and check-range

* change _pointer to mean a reference to non-GCed memory; add _gcpointer

* New `scheme/vector' library.

* scheme/unsafe/ops? (wasn't mentioned last time)

* Add `in-port', `port->list', `file->list'.

* upgrade Boehm GC to v7.1
----------------------------------------------------------------------

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!